(a) Field of the Invention
The present invention relates to a signal modulating device and a signal transmitting method.
(b) Description of the Related Art
Source data to be transmitted are encoded, modulated according to a channel characteristic of a transmission medium, and then transmitted.
Of the modulation methods, quadrature amplitude modulation (QAM) simultaneously combines and modulates the amplitude and the phase of a carrier so as to improve transmission efficiency in a frequency bandwidth. In detail, the QAM method uses a carrier configured by a sine wave and a cosine wave having the same frequency and a phase difference of 90° to amplitude modulate the in-phase and quadrature components, combine them, and transmit them.
In this instance, the signal is modulated by determining the positions of data to be arranged on a plane having the in-phase components as the horizontal axis and the quadrature component as the vertical axis (i.e., mapping), and the mapping process is usually performed by gray codes. A gray code represents a binary numeral system in which two successive values differ in only one bit.
In addition, as the wireless communication technology advances, demands for data transmission security as well as demands for high data transmission speeds have increased. Therefore, information security is to be maintained by satisfying appropriate data transmission speeds for the legitimate receivers, and maximizing information equivocation for illegal receivers who are wiretappers. For this, the required characteristic is the BER (bit error rate) performance that decreases steeply as the signal-to-noise ratio (SNR) increases.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.